Target electrode assembly



Nov. 3, 1964 A. c. KOERT TARGET ELECTRODE ASSEMBLY Filed Feb. 9. 1961 FIG.|.

United States Patent 3,155,859 TARGET ELECTRQDE ASSEMBLY Alvah C. Koert, Aiplaus, N.Y., assignor to General Electric Company, a corporation of New York Filed Feb. 9, 1961, Ser. No. 88,076 3 Claims. (Cl. 313-68) The present invention relates to improvements in target electrode assemblies of picture signal generating tubes, such as image orthicon tubes and the like.

Prior art picture signal generating tubes of the image orthicon type conventionally employ a target electrode on which an electron charge pattern representative of the light image input to the tube is formed. A preferred type of such target electrode may consist of an extremely thin, e.g. of the order of 500 angstrom units thick, film or membrane of polycrystalline and semi-conductive material having desirably large secondary electron emission, such as for example magnesium oxide. In the manufacture of such thin film target electrodes it is convenient to first deposit a film of the parent metal from which the oxide can be derived, e.g, magnesium, on a temporary supporting substrate of volatilizable material such as nitrocellulose. The metallic film and temporary substrate is then subject to a heat treatment or bakeout in an oxidizing atmosphere such as air at an elevated temperature of the order of 400 to 500 degrees centigrade for a period of a few hours, which both converts the metallic film to its desired oxide form and volatilizes and drives olf the temporary supporting substrate.

Desirably the thin film target is permanently supported only at its periphery by a supporting rim or ring of metallic material having a diameter comparable to that of the entire target electrode assembly. The supporting ring is chosen to have a thermal coeificient of expansion which closely matches that of the target membrane itself such as to maintain the target in a substantially taut condition not only during manufacture of the tube but also during the temperature cycling inherent in later operation of the tube. Accordingly the thermal coefficient of expansion and contraction of the supporting ring is an important criterion for its successful and proper functioning both during the manufacture and subsequent operation of the tube.

It has been discovered that certain materials having thermal coeificients of expansion such as to make them desirable for use as target support members, have an unfortunate tendency, when subjected to the heat treatment above mentioned, to oxidize at least on the surface portions thereof and form thereby an oxide which migrates, apparently by sublimation, and deposits on the nearby or peripheral portion of the target. This results in a deleterious coating on the peripheral portions of the target which undesirably reduces the effective area of the target.

Certain remedies have been suggested for this problem, among which is the plating or jacketing of the target support ring with a material which is highly resistant to oxidation or whose oxide is highly resistant to sublimation onto the adjacent area of the target, such jacket being of sufiicient thinness so that the overall coefficient of expansion of the resulting composite support ring is not adversely affected. This proposal has certain drawbacks however, in that it is difiicult to obtain suitable adherence of the jacket material to the core, and such a composite support ring undesirably increases the cost of the target assembly. Moreover it has been found that when the jacketing metal is made thick enough to preclude formation of the deleterious deposit on the target during the air bakeout, the thermal coeflicient of the composite support ring is significantly changed from that desired.

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Hence the foregoing remedy is not in all respects satisfactory.

It is a principal object of the present invention, therefore, to provide an improved target assembly for picture signal generating tubes of the image orthicon type or the like.

Another object is to provide, in such a target assembly having an exclusively peripherally supported membranelike target, a target support ring of substantially homogeneous composition throughout and consisting of a metallic material having both a desirable thermal coefiicient of expansion and desirable resistance to the formation of sublimeable oxides during the high temperature oxidizing atmosphere heat treatment portion of the target electrode manufacturing process.

Another object is to provide an improved target electrode support ring for an exclusively peripherally supported homogeneous polycrystalline semi-conductive oxide camera tube target electrode, which support ring is of homogeneous one-piece construction having a desirably minimal tendency to form a sublimeable oxide on the surface thereof and having a thermal coefficient of expansion and contraction such as to desirably match that of the target electrode.

These and other objects of my invention will be apparent from the following description including the accompanying drawing wherein:

FIGURE 1 is a transverse sectional view of a target electrode assembly constructed in accordance with my invention;

FIGURE 2 is an enlarged fragmentary sectional view of a portion of the structure of FIGURE 1.

Referring to the drawing, a target electrode assembly constructed in accordance with my invention includes a thin film target electrode 1 consisting of a membrane comprising a plurality of substantially contiguous crystals of semi-conductive material such as magnesium oxide. Such a target electrode, together with a method of manufacturing the same, is described in detail in U.S. Patent 2,922,907 commonly assigned herewith. The target electrode is secured directly to, and supported exclusively at its peripheral portion by, an annular supporting rim or ring member 2. The support ring 2 is in turn secured to an annular holder 3, here shown as of L-shaped cross section.

In accordance with my invention the support ring is made of a homogeneous metallic material throughout, which material both desirably matches the thermal coeflicient of expansion and contraction of the target electrode membrane and has a sufficient resistance to oxidation or to formation of sublimeable oxide during the 400500 C. air bakeout of the target during manufacture as to avoid transfer or deposition of oxide or other foreign materials onto the target electrode membrane. The average thermal coefiicient of expansion of such material lies between 5.71 x 10- and 6.21 x 10' inches per inch per degree centigrade from 30 C. to 500 C. One such suitable material for the support ring 2 is the iron-nickel-cobalt alloy or intermetallic compound commonly known as, and available commercially as, Fernico. Exemplary percentage constituents of such alloy, by weight, are approximately 53-54% Fe, 28.529.5% Ni, l6.5-17.5% Co. Target electrode assemblies made with such iron-nickel-cobalt alloy support rings have the desired compatibility of thermal expansion coeflicient between the support ring 2 and target membrane itself, and also in practice have been found to provide target assemblies which, upon completion of the oxidizing atmosphere bake-out phase of manufacture, are completely free of deleterious foreign deposits on the target electrode.

It will be appreciated by those skilled in the art that the invention may be carried out in various ways and may. take various forms. and embodiments other than those illustrative embodiments heretofore described. Accordingly it is to be understood that the scope of the invention is not? limited by the details of the foregoing description, but will be defined in the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is: v

1. A target electrode assembly for a picture signal generating tube or the like comprising an electric charge storage membrane of substantially contiguous crystals of semi-conductive metal oxide, an annular support ring secured to and forming the exclusive support for said membrane, said support ring being composed throughout of a homogeneous intermetallic compound of metals from the group consisting of iron, nickel and cobalt and having a thermal expansion coelficient averaging between 5.71 x 10- and 6.21 x 10- inches per inch per degree centigrade'from 30 C. to 500 C.

2. A target electrode assembly for a picture signal generating tube or the like comprising an electric charge storage membrane of substantially contiguous crystals of semi-conductive magnesium oxide having a thickness of the order of 500 to 1000 angstroms, an annular support ring having an inside diameter approximately equal to g the diameter of the target assembly. secured to the peripheral portion of and forming the exclusive support for said membrane, said support ring being composed throughout of a homogeneous intermetallic compound of metals from the group consisting of iron, nickel and cobalt and having a thermal expansion coefficient averaging between 5.71 x 10 and 6.21 x 10- inches per degree Centigrade from 30 C. to 500 C.

3. In a target electrode assembly for a picture signal generating tube or the like, a target electrode including an electric charge storage continuous membrane of homogeneous polycrystalline semi-conductive magnesium oxide, and a ring secured to said membrane and providing the exclusive support for said membrane, said ring consisting throughout of an alloy of approximately 53-54% iron by Weight, approximately 28.529.5% nickel by weight and approximately 16.5-17.5 cobalt by weight.

References Cited in the file of this patent UNITED STATES PATENTS 1,649,907 Mayer Nov. 22, 1927 2,277,440 Knochel Mar. 24, 1942 2,796,563 Ebers et a1. June 18, 1957 2,825,014 Willemse Feb. 25, 1958 2,922,907 Hannam Jan. 26, 1960 3,090,881 Wellinger May 21, 1963 

1. A TARGET ELECTRODE ASSEMBLY FOR A PICTURE SIGNAL GENERATING TUBE OR THE LIKE COMPRISING AN ELECTRIC CHARGE STORAGE MEMBRANE OF SUBSTANTIALLY CONTIGUOUS CRYSTALS OF SEMI-CONDUCTIVE METAL OXIDE, AN ANNULAR SUPPORT RING SECURED TO AND FORMING THE EXCLUSIVE SUPPORT FOR SAID MEMBRANE, SAID SUPPORT RING BEING COMPOSED THROUGHOUT OF A HOMOGENEOUS INTERMETALLIC COMPOUND OF METALS FROM THE GROUP CONSISTING OF IRON, NICKEL AND COBALT AND HAVING A THERMAL EXPANSION COEFFICIENT AVERAGING BETWEEN 5.71 X 10-**6 AND 6.21 X 10-**6 INCHES PER INCH DEGREE CENTIGRADE FROM 30*C. TO 500*C. 